FIELD OF THE INVENTION
The invention relates to a method for authentication between two electronic devices, such as data stations.
One such method is known, for instance, from U.S. Pat. No. 3,761,892. In such a system, data are transmitted from one station to the other, and then the datum is encrypted with a code key by the second data station to make a cryptogram and is finally sent back to the first data station. The first station checks whether or not the cryptogram is correct, that is whether or not the code key known to the first station was used, which means that the data station is accordingly authorized access.
U.S. Pat. No. 3,761,892 explains that it is highly desirable for the system to remain inoperative until such time as the complete data set/cryptogram has been transmitted, even if the first part, or some other part, of the cryptogram does not match an authorized cryptogram. Proceeding in that way is surely appropriate for some kinds of data stations, but in the case of portable chip cards, for instance, that kind of complete transmission of the cryptogram can mean that a non-legitimate user with a valid card could observe the transmission of authentication procedures using his or her own equipment, and could finally simulate a valid card from the data learned.